The present invention relates to a distance detection apparatus and a method therefor, both suitable for detecting a relative distance between mobile stations or a relative distance between a mobile station and a base station. In particular, the present invention relates to a distance detection apparatus and a method therefor, both suitably applicable to a mobile communication system in conformity with the spectrum spreading communication mode.
Conventionally, there has been developed a distance detection apparatus for detecting a relative distance between two mobiles by means of the communication conforming to the spectrum spreading communication mode. For example, in the vehicle communication apparatus disclosed in Japanese Laid-Open Publication No. HEI 5-122120, when a certain communication station MS-1 transmitted a radio wave modulated in conformity with the spreading modulation to another communication station MS-2 and the communication station MS-2 received the transmitted wave, the communication station MS-2 transmits a radio wave modulated in conformity with the spreading modulation by the use of a spreading code synchronized with the spreading code of the received wave back to the communication station MS-1.
When the communication station MS-1 received the responded wave from the communication station MS-2, the communication station MS-1 detects the period of time from the transmission of the radio wave to the reception of the responded wave from the communication station MS-2, and detects the relative distance between the communication station MS-1 and the communication station MS-2 on the basis of the following formula (1).
Relative Distance=(Light velocity)xc3x97(Time Difference)/2xe2x80x83xe2x80x83(1)
However, the aforesaid vehicle communication apparatus has a problem that it cannot perform the distance detection with high accuracy owing to signal delays in the transmission circuits thereof and the reception circuits thereof.
The present invention was invented in consideration of the problem, and aims to provide a method for detecting distance and a distance detection apparatus, both capable of removing the errors of distance detection caused by signal delays in the transmission circuits thereof and the reception circuits thereof.
A method for detecting a distance according to the present invention is a method for detecting a distance by measuring the propagation time of an electromagnetic wave, and the method inputs a transmission signal output from a transmission system circuit directly into a reception system circuit, and obtains the signal delay time of the transmission and reception circuit by measuring a difference between the reception timing of the transmission signal that has passed through the reception system circuit and the transmission timing of the transmission signal, and then performs the correction of the measured distance by using the obtained signal delay time.
According to the method, the sum of the signal delay time of the transmission system circuit and the signal delay time of the reception system circuit are measured, and the measured sum of the signal delay times is used as a correction value at the time of obtaining a measurement distance. Consequently, respective signal delay times of the transmission system circuit and the reception system circuit are canceled. Thereby, distance detection with high accuracy becomes possible.
Moreover, a method for detecting a distance according to the present invention receives a reflection signal of a transmission signal from an object of distance measurement, and measures the phase difference between the reception signal and the transmission signal, and detects the relative distance to the object of distance measurement on the basis of the measurement result, and further corrects the detected relative distance by means of the signal delay time in a transmission and reception circuit, the signal delay time being a measurement result of the difference between the reception timing of the transmission signal in the reception system circuit and the transmission timing of the transmission signal.
According to the method, the sum of the signal delay time of the transmission system circuit and the signal delay time of the reception system circuit is measured, and the measured sum of the signal delay times is used as a correction value at the time of obtaining a measurement distance to the object of distance measurement. Consequently, respective signal delay times of the transmission system circuit and the reception system circuit are canceled. Thereby, distance detection with high accuracy becomes possible.
Moreover, a distance detection apparatus according to the present invention adopts a configuration comprising: a transmission system circuit in which a timer of a self station generates a periodic signal that is transmitted to an opponent station; a reception system circuit for receiving a periodic signal generated by a timer of the opponent station and transmitted to the self station; a signal path for inputting the transmission signal from the transmission system circuit to the reception system circuit directly; and a distance detection section for measuring a difference between the transmission timing at the time of the transmission of the signal from the transmission system circuit and the reception timing at the time of the input of transmission signal to the reception system circuit through the signal path to obtain a self station signal delay time, and for measuring a quantity of discrepancy between a reception timing of the transmission signal from the opponent station and the reference timing of the timer of the self station to obtain a self station detection phase difference, and for detecting a relative distance between the self station and the opponent station by the use of the self station signal delay time, the self station detection phase difference, the opponent station signal delay time obtained by the opponent station, and the opponent station detection phase difference.
According to the configuration, by the measurement of the respective sums of the signal delay times of the transmission system circuits and the signal delay times of the reception system circuits of the two communication stations, and by the use of the respective sums of the signal delay times as correction values at the time of the obtainment of a relative distance between the two communication stations, signal delay times of the respective transmission system circuits and the respective reception system circuits of the two communication stations are canceled, and then distance detection with high accuracy becomes possible.